Automatic transmission

ABSTRACT

Second and third clutches are axially aligned so that the back side of the second clutch and the front side of the third clutch oppose each other, and a first clutch is positioned radially inward of the second and third clutches. Further, a clutch drum is extended so as to be used in common by the second and third clutches, the second clutch is engaged and disengaged from the axial front side by a second piston of a second oil pressure actuator, and the third clutch is engaged and disengaged from the axial rear side by a third piston of a third oil pressure actuator. The first through third clutches are positioned in a compact manner and can be independently operated.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to an automatic transmission for anautomobile, and is particularly applicable to an automatic transmissionin which plural clutches are closely positioned. More particularly, theinvention relates to the structure of such a clutch section.

[0003] 2. Related Art

[0004] Automatic transmissions for vehicles, such as automobiles havinga structure wherein plural clutches are closely (“collectively”)positioned are known. For example, a structure in which three clutchesC1, C2 and C3 that operate independently when a vehicle moves forwardand that are collectively disposed on the front side of a gear sectionhaving a plurality of planetary gear units is disclosed in FIG. 5 andFIG. 7 of Japanese Patent Application Laid-Open No. 4-285347. Thisstructure is capable of providing six forward shift speeds because, asmentioned above, each of the three clutches C1, C2 and C3 isindependently operated.

[0005] While multi-speed automatic transmissions are in demand in orderto improve fuel consumption, greater compactness is also demanded.However, a greater number of speeds and compact size are not compatiblein an automatic transmission.

[0006] In the above-mentioned related art, in order to independentlyoperate the three clutches C1, C2 and C3, the three clutches C1, C2 andC3 need to be independently structured. However, because it is necessaryto combine the positions of the three clutches C1, C2 and C3 to providean engagement state for each shift speed, it is difficult to have acompact structure. Therefore, even if the six forward shift speeds areachieved, the overall size of the automatic transmission is increased.In other words, it is difficult to achieve a multi-speed transmission ina compact size with the structure shown in the above-mentioned relatedart.

SUMMARY OF THE INVENTION

[0007] Accordingly, an object of the invention is to provide anautomatic transmission in which three clutches that engage when movingforward are positioned in close proximity (“collectively positioned”)and two clutches are radially aligned, with the third clutch positionedradially inward of the other two clutches, thereby solving theabove-mentioned problems. In other words, the object of the invention isto provide an automatic transmission having both multiple speeds andcompactness.

[0008] In one aspect the present invention (for example, refer to FIG. 1and FIG. 3), provides an automatic transmission that extends from afront end to a rear end and that changes the power transfer path througha gear assembly, and thereby changes the rotational speed of an inputmember to one of a plurality of shift speeds (for example, six forwardspeeds and one reverse speed). The transmission transmits the rotationof the input member to an output member using a clutch and a holdingunit. At least a first clutch, a second clutch and a third clutch whichtransfer the rotation of the input member to different rotationalelements of the gear assembly, and which are engaged when moving forwardare collectively positioned along with a first oil pressure actuator, asecond oil pressure actuator, and a third oil pressure actuator,respectively operating the three clutches, to form a clutch section. Thesecond and third clutches are axially aligned so that the back side ofthe second clutch and the front side of the third clutch oppose eachother, and the first clutch is positioned radially inward of the secondand third clutches. An axially extended drum portion serves as a clutchdrum for both the second and third clutches. By engaging and disengagingthe second clutch from the axial front side using the second oilpressure actuator, and by engaging and disengaging the third clutch fromthe axial back side using a third oil pressure actuator, the first,second and third clutches are separately engaged and disengaged by thefirst, second and third oil pressure actuators, respectively.

[0009] By axial alignment of the second and third clutches so that theback side of the second clutch and the front side of the third clutchoppose each other, and by positioning the first clutch radially inwardof the second and third clutches, the three clutches are compactlypositioned, the axial dimension can be shortened and the automatictransmission can be made more compact overall.

[0010] Also, because the second and third clutches share a drum incommon, one clutch drum can be omitted and the number of parts isthereby reduced and the automatic transmission made more compact.

[0011] Further, by engaging and disengaging the second clutch from thefront side by the second oil pressure actuator, and by engaging anddisengaging the third clutch from the back side using the third oilpressure actuator, even when the clutch drum is shared in common asdescribed above, the second and third clutches can be separately engagedand disengaged by the second and third oil pressure actuators,respectively. In other words, the first, second and third clutches caneach be independently operated. This makes it possible to increase thenumber of shift speeds by one speed. For example, a transmission thatconventionally had five forward speeds can be made to have six forwardspeeds.

[0012] The automatic transmission according to the present invention maybe structured such that a clutch drum has a flange portion on its frontend side, which flange is sandwiched between a second piston of thesecond oil pressure actuator positioned on the back side, and a thirdpiston of the third oil pressure actuator positioned on the front side.Further, a portion of the third piston is axially extended to the backside, along the outer surface of the drum to the back side of the thirdclutch for engaging same. Therefore, according to the present invention,by sandwiching the flange portion of the shared clutch drum between thesecond piston of the second oil pressure actuator positioned on the backside, and the third piston of the third oil pressure actuator positionedon the front side, and further, by axially extending a portion of thethird piston to the back side axially along the outer surface of thedrum to the back side of the third clutch, the second clutch can beoperated from its front side by the second piston, and the third clutchcan be operated from its back side by the third piston. In other words,the second clutch is pressed from the front side, toward the back side,by the second piston, and, in reverse, the third clutch is pulled fromthe back side to the front side by the third piston, whereby they can beengaged and disengaged. By adopting this structure, the automatictransmission can be made very compact, and it is possible toindependently operate the second and third-clutches. In other words, thethird oil pressure actuator has its oil pressure chamber, and pistonhead therein, located at one axial end of the second clutch and a pistonextension, in the form of a drum or skirt, extends from the piston head,axially along ran exterior (outer) surface of the drum shared by thesecond and third clutches, to an engaging element or flange portionlocated at an axial end of the third clutch for engaging the thirdclutch. Thus, the head and engaging element of the third piston areaxially opposed, at opposite ends of the axially aligned second andthird clutches.

[0013] The automatic transmission according to the present invention mayalso be structured such that a second oil pressure chamber is formedbetween a flange portion of the clutch drum and the second piston, and athird oil pressure chamber is formed between the flange portion and thethird piston. Therefore, in accordance with the present invention, byforming the second oil pressure chamber between the flange portion ofthe clutch drum and the second piston, and by forming the third oilpressure chamber between the same flange portion and the third piston,in addition to the shared use of the clutch drum by the second and thirdclutches as described above, the oil pressure actuators can share aportion in common, which allows the automatic transmission to be madeeven more compact.

[0014] The automatic transmission of the present invention may bestructured such that the rotational speed of the input member is changedto the highest speed (for example, sixth speed) from among the pluralityof shift speeds and the rotation is transmitted to the output member bydraining the oil pressure of the third oil pressure chamber to disengagethe third clutch. Therefore, in the present invention, shifting to thehighest speed is achieved by draining the oil pressure from the thirdoil pressure chamber to disengage the third clutch while the secondclutch remains engaged. As a result, as described in more detail later,it is possible to increase the number of shift speeds by one speed.

[0015] The automatic transmission according to the present invention mayhave the first clutch positioned so that it and the third clutch axiallyoverlap, with the first clutch radially inward of the third clutch.Therefore, according to the present invention, the position of the firstclutch, which is on the inner side of the second and third clutches, isfurther limited, and the first clutch is positioned so it and the thirdclutch respectively axially overlap on the inner side of the thirdclutch.

[0016] The automatic transmission of the present invention may have athird hub of the third clutch positioned on the inner side of the thirdclutch, a second hub of the second clutch positioned on the inner sideof the third hub, and the first clutch positioned on the inner side ofthe second hub. In other words, the third clutch, the third hub, thesecond hub and the first clutch are positioned in order from theradially outer side to the inner side, i.e., toward the axial center ofthe transmission.

[0017] The automatic transmission of the present invention may bestructured such that the first clutch is engaged at or below one forwardspeed in a directly connected stage (for example, the fourth speed), thesecond clutch is engaged at or above that same speed in the directlyconnected stage, the third clutch is engaged in at least one of theforward speeds (for example, the third speed and the fifth speed) and inthe reverse speed, whereby at least five forward speeds and one reversespeed are achieved. Therefore, according to the present invention, byengaging the first clutch at or below the directly connected stage,engaging the second clutch at or above the directly, connected stage,and engaging the third clutch for at least one forward speed, fiveforward speeds and one reverse speeds are achieved. In other words, itis possible to make the automatic transmission more compact whileachieving these six speeds.

[0018] The automatic transmission according to the present invention mayhave the first clutch engaged in the first through fourth forwardspeeds, the second clutch engaged in at least the fourth and fifthspeeds, the third clutch engaged in the third and fifth forward speedsand in reverse speed, to achieve at least five forward speeds and onereverse speed. Therefore, shift speeds at which the first, second andthird clutches are engaged are further limited, and the first, secondand third clutches are engaged in the first through fourth speeds, thefourth and fifth speeds, and the third and fifth speeds, respectively.

[0019] Further, the automatic transmission according to the presentinvention may have the first piston of the first actuator positioned onthe axial front side of the first clutch, and on the inner side of thesecond clutch.

[0020] In preferred embodiments the automatic transmission of thepresent invention may have a first cancel plate that defines a firstcancel chamber between itself and the first piston and that ispositioned at the rear side of the first piston. The first clutch drumhas a flange portion that defines a first oil pressure chamber betweenitself and the first piston and that is positioned on the front side ofthe first piston. A second cancel plate of the second actuator ispositioned on the front side of the flange portion of the first clutchdrum, while the second piston defines a second cancel chamber betweenitself and the second cancel plate and is positioned on the front sideof the second cancel plate, and a flange portion of the clutch drum ofthe second and third clutches, defining a second oil pressure chamberbetween itself and the second piston, is positioned on the front side ofthe second piston. Therefore, according to such embodiments of theinvention, because the second cancel chamber is formed between thesecond cancel plate and the second piston, allowing compactness of theclutch section, and the oil pressure that is supplied to the secondclutch can be reliably canceled.

[0021] Further, the automatic transmission according to the presentinvention may include a first planetary gear unit that is a dualplanetary gear unit and second and third planetary gear units that aresimple planetary gear units, the first, the second, and third planetarygear units being interposed between the first, the second and the thirdclutches and the output member; and first, second, third and fourthholding units that are engaged and disengaged with rotational elementsof the first, the second and the third planetary gear units. The firstholding unit is a combination of a first brake and a first one-wayclutch, the second holding unit is a second brake, the third holdingunit is a combination of a third brake and a second one-way clutch; andthe fourth holding unit is a combination of a fourth brake and a thirdone-way clutch. Further, in such embodiments a member (intermediateshaft) on the output side of the first clutch may be; integrally formedwith sun gears of the second and the third planetary gear units, amember (second sleeve shaft) on the output side of the second clutch maybe integrally formed with a carrier of the second planetary gear unitand a ring gear of the third planetary gear unit is engaged anddisengaged by the fourth holding unit. Still further, the member on theoutput side of the third clutch may be integrally formed with a sun gearof the first planetary gear unit which is engaged and disengaged by thethird holding unit. The first holding units may be engaged with anddisengaged from a carrier of the first planetary gear set and the ringgears of the first and second planetary gear sets may be integrallyformed and engaged and disengaged by the second holding unit. A carrierof the third planetary gear set may be integrally formed with the outputmember. A first forward speed is achieved by engagement of the firstclutch and the fourth holding units, a second forward speed is achievedby the engagement of the first clutch and the first and the thirdholding units, a third forward speed is achieved by engagement of thefirst and the third clutches and the first holding units, a fourthforward speed is achieved by engagement of the first and the secondclutches, a fifth forward speed is achieved by engagement of the secondand third clutches and the first holding units, and reverse speed isachieved by engagement of the third clutch and the first and the fourthholding units. Therefore, the clutch section is compact, and it ispossible to provide the automatic transmission with five forward speedsand one reverse speed.

[0022] The automatic transmission of the present invention may also havea sixth forward speed achieved by the engagement of the second clutchand the second holding unit. Therefore, according to the presentinvention, the clutch section is compact and allows for six forwardspeeds and one reverse speed.

[0023] The automatic transmission according to other preferredembodiments of the present invention has the fourth clutch axiallyaligned with and located on the front side of the first clutch. Further,the input side elements of the first and fourth clutches are integrallystructured, the output side member of the fourth clutch and the sungears of the second and third planetary gear units are integrallystructured, and a one-way clutch is interposed between the output sidemember of the first clutch and the output side member of the fourthclutch. Therefore, because shifting between the fourth and fifth speedscan be carried out using the one-way clutch, it is possible to improvecontrol. Also, a transmission in which the four clutches (first, second,third and fourth clutches) are collectively positioned can be compactlystructured and at least the first and third clutches can beindependently operated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a cross-section of an entire automatic transmissionaccording to a first embodiment of the present invention;

[0025]FIG. 2 is an expanded cross-section of a torque converter portionof the first embodiment;

[0026]FIG. 3 is an expanded cross-section of a clutch assembly thatis-the front section of a multi-speed change mechanism of the firstembodiment;

[0027]FIG. 4 is an expanded cross-section of a gear assembly that isa-rear section of the multi-speed change mechanism of the firstembodiment;

[0028]FIG. 5 is a skeletal diagram of the multi-speed change mechanismof the first embodiment;

[0029]FIG. 6 is a diagram illustrating operation of the multi-speedchange mechanism of the first embodiment;

[0030]FIG. 7 is a speed diagram of the multi-speed change mechanism ofthe first embodiment;

[0031]FIG. 8 is an expanded cross-section that shows the clutch assemblythat is the front section of the multi-speed change mechanism of asecond embodiment;

[0032]FIG. 9 is a skeletal diagram of the multi-speed change mechanismof the second embodiment; and

[0033]FIG. 10 is a diagram illustrating operation of the multi-speedchange mechanism of the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] A first embodiment of the invention will be described withreference to FIGS. 1-7. In FIG. 1 through FIG. 4, the left side is thefront side (forward) and the right side is the rear side (back side).

[0035] The automatic transmission, as shown in FIG. 1, is provided witha torque converter 2, and a multi-speed change mechanism 6 having threeplanetary gear sets (a first planetary gear set 3, a second planetarygear set 4, and a third planetary gear set 5), wherein the torqueconverter 2 and the multi-speed change mechanism 6 are aligned on oneaxle, and is housed in a case that integrates a converter housing 7 anda transmission case 9.

[0036] The torque converter 2, as shown in FIG. 2, is provided with apump impeller 11 fixed to a cover 10 that is connected to an engineoutput shaft (not shown), a turbine runner 13 that connects to an inputshaft 12 of the multi-speed change mechanism 6, and a stator 16 that issupported via a one-way clutch 15. A lock-up clutch 19 mechanicallyconnects, via a spring damper 17, the cover 10 and the input shaft 12.Also, a pump case 20 is fixed between the converter housing 7 and thetransmission case 9 (refer to FIG. 1), and an oil pump 21 is provided inthe pump case 20. Further, a pump cover 22 is fixed to the rear side(backside; right side in FIG. 2) of the pump case 20, and an inner raceof the above mentioned one-way clutch 15 is fixed to the pump cover 22.

[0037] As shown in FIG. 1, for the multi-speed change mechanism 6, afront side or forward section (torque converter side) has a clutchassembly 23, and a back side or rear side section (output shaft side)has a gear assembly 24.

[0038] Three clutches, a first clutch C1, a second clutch C2, and athird clutch C3 and their oil pressure actuators (oil pressure servos)are collectively positioned in the clutch section 23. The second andthird clutches C2 and C3 are positioned at the outer circumference ofthe transmission with the second clutch C2 on the axially forward sideand the third clutch C3 on the axial back side. The second and the thirdclutches are axially aligned, with the back side of the second clutchand the front side of the third clutch opposing each other. The firstclutch C1 is positioned radially inward of the second and third clutchesC2 and C3. More specifically, the first clutch C1 is positioned radiallyinward of the third clutch C3 without axially overlapping the secondclutch C2.

[0039] Clutch Section

[0040] Hereinafter, the clutch section 23 will be described in detailwith reference to FIG. 3 (expanded view of the clutch section 23 in FIG.1).

[0041] The first, second and third clutches C1, C2 and C3 are rotatablysupported by a boss portion 22 a of the pump cover 22, and rotation istransmitted to pump cover 22 from a sleeve 25 which is connected to theinput shaft (input member) 12.

[0042] A flange portion 26 a of a first clutch drum 26 of the firstclutch C1 is fixed to the backside of the sleeve 25. A drum portion 26 bextends axially from the outer periphery of the flange portion 26 atoward the back side. An axially extending spline 26 c is formed on theinner surface of the drum 26, and a plurality of drive plates (outerfriction plates) 27 are engaged by the spline 26 c. A plurality ofdriven disks 29, with which the drive plates 27 are interleaved and areengaged and disengaged, are engaged by axially extending spline 30 athat is formed on the outer surface of a first, hub 30. The innerperiphery of the first hub 30 is connected and fixed to an intermediateshaft 31.

[0043] The first oil pressure actuator (servo) that engages anddisengages the first clutch C1 has a first piston 32 that is positionedon the back side of the flange portion 26 a of the first clutch drum 26.The first piston 32 is movably supported in the axial direction by thefirst clutch drum 26 and a peripheral surface of the input shaft 12, andan oil-tight first oil pressure chamber 33 is formed between the firstpiston 32 and the flange portion 26 a of the first clutch drum 26. Arear end portion 32 a at the outer periphery of the first piston 32 ispositioned to engage (press against) the front side of the first clutchC1. A first cancel plate 34 is fixed to the input shaft 12 and extendstherefrom the backside of the first piston 32. A return spring 35 iscompressed between a front surface of the first cancel plate 34 and arear surface of the first piston 32 which define therebetween a firstcancel chamber 36 that offsets (counters) oil pressure that is suppliedto the first oil pressure chamber 33.

[0044] The first clutch C1 is engaged when a predetermined oil pressureis supplied to the first oil pressure chamber 33 with the input shaft 12rotating, and the first piston 32 moves to the back side against theforce of the return spring 35. The rotation of the output shaft 12 istransmitted at the same speed to the intermediate shaft 31.

[0045] Next, the second and third clutches C2 and C3 will be describedin detail.

[0046] A flange portion 37 a of a clutch drum 37 for the second andthird clutches C2 and C3 is fixed, slightly ahead of axial center on theperipheral surface of the sleeve 25. A drum portion 37 b extends axiallytoward the backside from the flange portion 37 a. A spline 37 c isformed on the inner surface of the drum portion 37 b. On the front sideof the spline 37 c engages a plurality of drive plates (outer frictionplates) 39 of the second clutch C2 and on the back side engages aplurality of drive plates (outer friction plates) 40 for the thirdclutch C3. In other words, the clutch drum 37 is axially extended toaccommodate the drive plates 39 and 40 of the second and third clutchesC2 and C3 in an axially aligned arrangement. A stopper plate that is notaxially movable is attached to the spline 37 c, slightly to the backside of the drive plate 39 which is the rear most (back side) among theplurality of drive plates 39, and slightly to the front side of thedrive plate 40 that is the front most of the plurality of drive plates40. Thus, the second and third clutches C2 and C3 can be independentlyoperated.

[0047] A plurality of driven disks 41, with which the drive plates 39 ofthe second clutch C2 are engaged and disengaged, are engaged in anaxially extending array on a spline 42 a that is formed on the outersurface of a second hub 42. The inner side of the second hub 42 isconnected and fixed to a second sleeve shaft 43 that is rotatablysupported by the intermediate shaft 31.

[0048] A plurality of driven disks 44, with which the drive plates 40 ofthe third clutch C3 are engaged and disengaged, is engaged in an axialarray with a spline 45 a that is formed on the outer surface of a thirdhub 45. The inner side of the third hub 45 is connected and fixed to athird sleeve shaft 46 that is rotatably supported by the second sleeveshaft 43.

[0049] The second oil pressure actuator that engages and disengages thesecond clutch C2 has a second piston 47 that is positioned on thebackside of the flange portion 37 a of the clutch drum 37. The secondpiston 47 is supported for axial movement by the clutch drum 37 and theouter peripheral surface of the sleeve 25, and an oil-tight second oilpressure chamber 49 is formed between the second piston 47 and theclutch drum 37. A rear edge portion 47 a on the outer side of the secondpiston 47 extends axially to oppose the front surface of the secondclutch C2. A second cancel plate 50 whose inner periphery is fixed tothe outer peripheral surface of the sleeve 25 is provided on the backside of the second piston 47. A return spring 51 is compressed betweenthe front surface of the second cancel plate 50 and the back surface ofthe second piston 47 which define a second cancel chamber 52therebetween that offsets the centrifugal oil pressure that is suppliedto the second oil pressure chamber.

[0050] The third oil pressure actuator that engages and disengages thethird clutch is provided with a third piston 53 that has a flangeportion 53 a that is positioned on the front side of the flange portion37 a of the clutch drum 37. Further, the third piston 53 has a drumportion 53 b that extends toward the backside from the outer peripheryof the flange portion 53 a along the external side of the clutch drum37. Splines 53 c, engaged with the splines (not shown) formed on theouter peripheral surface of the drum portion 37 b, are formed on theinterior surface of the drum portion 53 b, and a portion 53 d on theback side is positioned so as to oppose (correspond to) the back side ofthe third clutch C3. A third cancel plate 54 whose inner periphery isfixed to the front side of the outer peripheral surface of the sleeve 25is provided on the front side of the flange portion 53 a of the thirdpiston 53. The third piston 53 is movably supported by the clutch drum37, the third cancel plate 54 and the outer peripheral surface of thesleeve 25. An oil-tight third oil chamber 55 is formed between thebackside of the flange portion 53 a of the third piston 53 and the frontside of the flange portion 37 a of-the clutch drum 37. Further, a returnspring 56 is compressed between the front side of the flange portion 53a of the third piston 53 and the third cancel plate 54 which forms athird cancel chamber 57 that offsets the centrifugal oil pressure thatis supplied to the third oil pressure chamber 55.

[0051] Because the second and third clutches C2 and C3 are axiallyaligned so that the back side of the second clutch and the front side ofthe third clutch are opposed, because the first clutch is positionedradially inward of the second and third clutches C2 and C3, and furtherbecause a portion of the second and third clutches C2 and C3 is used incommon, the entire clutch portion 23 can be compactly structured.

[0052] More specifically, the first clutch C1 is positioned so that itaxially overlaps the third clutch and is radially inward of same. Also,the third hub 45 is positioned radially inward of the third clutch C3,the second hub 42 is positioned radially inward of the third hub 45, andthe first clutch C1 is positioned radially inward of the second hub 42.In other words, these members are positioned so that they axiallyoverlap and are radially arranged in the order of the third clutch C3,the third hub 45, the second hub 42 and the first clutch C1 from theouter side toward the center.

[0053] Moreover, by engaging and disengaging the second clutch C2 fromthe axial front side with the second piston 47 of the second oilpressure actuator, and by engaging and disengaging the third clutch C3from the axial rear (back) side by the third piston 53 of the third oilpressure actuator, the first, second and third clutches C1, C2 and C3can each be independently engaged and disengaged by the first, secondand third oil pressure actuators, respectively. In other words, when apredetermined oil pressure is supplied to the first oil pressure chamber33 with the input shaft 12 rotating, the first piston 32 overcomes theforce of the return spring 35 and moves toward the back side, and thefirst clutch C1 is engaged. Due to the engagement of the first clutchC1, the rotation of the output shaft 12 is transmitted to theintermediate shaft 31 via the first clutch drum 26, the first hub 30,etc. In the same way, when a predetermined oil pressure is supplied tothe second oil pressure chamber 49 with the input shaft 12 rotating, thesecond piston 47 overcomes the force of the return spring 51 and movestoward the back side, and the second clutch C2 is thereby engaged fromthe front side. Due to the engagement of the second clutch C2, therotation of the output shaft 12 is transmitted to the second sleeveshaft 43 via the clutch drum 37, the second hub 42, etc. Further, in thesame way, when a predetermined oil pressure is supplied to the third oilpressure chamber 55 with the input shaft 12 rotating, the third piston53 overcomes the force of the return spring 56 and moves toward thefront side, and the third clutch C3 is thereby engaged from the backside. Due to the engagement of the third clutch, the rotation of theoutput shaft 12 is transmitted to the third sleeve shaft 46 via theclutch drum 37, the third hub 45, etc.

[0054] In the above-described manner, the first, second and thirdclutches C1, C2 and C3 can each be independently operated (engaged anddisengaged) by the first, second and third oil pressure actuators.Further, by doing so, as described later, it is possible for automatictransmission 1 according to the invention to have six forward shiftspeeds.

[0055] Gear Section

[0056] As shown in FIG. 1, gear section 24 is provided on the rear(back) side of the multi-speed change mechanism 6, and three planetarygear units (the first planetary gear unit 3, the second planetary gearunit 4 and the third planetary gear unit 5 are closely (“collectively”)positioned along with their holding units (first through fourth holdingunits). Further, in the embodiment of the invention illustrated in FIG.1, the first holding unit is made up of a first brake B1 and a firstone-way clutch F1; the second holding unit is a second brake B2; thethird holding unit includes a third brake B3 and a second one-way clutchF2; and the fourth holding unit includes a fourth brake B4 and a thirdone-way clutch F3.

[0057] As shown in FIG. 4, the gear section 24 includes, in order fromthe front side (the input member 12 side), the first planetary gear unit3 that has a sun gear S1 formed on the third sleeve shaft 46, the secondplanetary gear unit 4 that has a carrier CR2 connected to the secondsleeve shaft 43, and the third planetary gear unit 5 that has a sun gearS3 formed on the intermediate shaft 31. Further, the third brake B3, thefirst one-way clutch F1 and the second one-way clutch F2 are positionedaxially between the clutch section 23 and the first planetary gear unit3, and the third one-way clutch F3 is positioned axially between thesecond planetary gear unit 4 and the third planetary gear unit 5.

[0058] The third brake B3 is a multi-plate brake, and includes aplurality of outer brake plates 61 engaged on spline 9 a formed on thetransmission case 9, and brake discs 65 splined to the hub 63 that isfixed to an outer race 62 of the second one-way clutch F2. The innerrace of the second one-way clutch F2 is formed by the third sleeve 46itself, and the third brake B3 and the second one-way clutch F2 axiallyoverlap in their radially spaced positions.

[0059] An oil pressure actuator 66 for the third brake is provided onthe axial rear side of the third brake B3, and the oil pressure actuator66 is made up of a cylinder member 67 that is connected to thetransmission case 9 such that the cylinder member 67 cannot axiallymove, and a piston 69 that is fitted in cylinder member 67 in anoil-tight manner, with a forward edge portion 69 a facing the thirdbrake B3. Further, an outer race 70 of the first one-way clutch F1 isspline-engaged with the inner surface of the cylinder member 67, and aninner race 71 of the first one-way clutch F1 is spline-engaged with aboss portion 72 of the carrier CR1 of the first planetary gear unit 3.The oil pressure actuator 66 for the third brake B3 and the firstone-way clutch F1 are positioned so that they (or at least portionsthereof) respectively axially overlap in radially different positions.Further, the end portion of the piston 69 is formed in a comblike shape,and a return spring 73 is held in position by the comb teeth. Further,the second one-way clutch F2 and the first one-way clutch F1 are axiallyaligned, and the third brake B3 and its oil pressure actuator 66 are onthe radially outward side, and are positioned to axially overlap thefirst and second one-way clutches F1 and F2.

[0060] The first planetary gear unit 3 is a dual planetary gear that hasa pinion P1 a that meshes with the sun gear S1 and a pinion P1 b thatmeshes with a ring gear R1 (refer to FIG. 5), and a carrier CR1 thatsupports the pinions P1 a and P1 b that mutually mesh is rotatablysupported on the third sleeve shaft 46 by the boss portion 72, and thesun gear S1 is integrally formed with the third sleeve shaft 46.Further, the ring gear R1 is rotatably supported by a plate 75 that isspline-engaged at the rear edge of ring gear R1 to, limit its axialmovement. R1 is also spline-engaged with a ring gear R2 of the secondplanetary gear unit 4.

[0061] The first brake B1 is a multi-plate brake, and includes aplurality of outer brake plates 76 engaged with a spline 9 b (formedcontinuous with spline 9 a) formed on the transmission case 9, and innerbrake discs 79 engaged with the spline that is formed on the outerperipheral surface of a cup-shaped member 80 that constitutes thecarrier CR1. The cup-shaped member 80 has an outer side flat surface 80a which extends so as to cover the side of the first planetary gear unit3. The spline that engages the inner brake discs 79 of the first brakeB1 is formed on the outer side of flat surface 80 a and is positioned sothat the first brake B1 and the first planetary gear unit 3 axiallyoverlap, with the first brake B1 located radially outward of the firstplanetary gear unit 3. More accurately, the first brake B1 is within theaxial length of the third planetary gear unit 3.

[0062] An oil pressure actuator 81 for the first brake is provided onthe rear side of the first brake B1. The oil pressure actuator 81 has acylinder 82, that is fixed to a small diameter step formed in thetransmission case 9, and a piston member 83 that is fitted in cylinder82 in an oil tight manner. The oil pressure actuator 81 is positionedaxially straddling and radially outward of the first and secondplanetary gear units 3 and 4. In other words, the first brake B1 thatholds a specified rotational element (CR1) of the first planetary gearunit 3 and the oil pressure actuator 81 are positioned on the outer sideof the first planetary gear unit 3, with at least a portion thereofaxially overlapping the first planetary gear unit 3. Further, the pistonmember 83 has a comblike portion facing the first brake B1, and a returnspring 85 is held between the comb teeth.

[0063] The second planetary gear unit 4 is a simple planetary gear unit,and includes a carrier CR2 that supports a pinion P2 and isspline-engaged with the second sleeve shaft 43. Also, a sun gear S2 issplined with the intermediate shaft 31, and the ring gear R2 is splinedwith the ring gear R1 of the first planetary gear 3. The secondplanetary gear unit 4 has a smaller diameter than that of the firstplanetary gear unit 3, the latter being a dual planetary gear unit.Consequently, a collar portion 86 extends radially outward to the frontedge of the ring gear R2 and the an outer periphery of the collar 86 issplined to the inner peripheral surface of the ring gear R1. The oilpressure actuator 81 for the first brake, excluding the extended portionof the piston, is positioned on the outer side of the second planetarygear unit 4, along with the second brake B2. Consequently, the oilpressure actuator 81, despite the fact that the transmission case 6 hasa small diameter due to a stepped diameter portion 9 c, has a specifiedpressure receiving surface area, and has a torque volume thatcorresponds to the torque capacity necessary for the first brake B1.

[0064] The second brake B2 is positioned on the rear side of the oilpressure actuator 81 for the first brake. The second brake B2 is amulti-plate brake, and includes a plurality of outer brake plates 87engaged by a spline 9 d inside the transmission case 9 and inner brakediscs 89 engaged with a spline that is formed on the outer peripheralsurface of the ring gear R2. The second brake B2 is positioned so as toaxially overlap the second planetary gear unit 4 and radially outward ofthe second planetary gear unit 4. More accurately, the second brake B2is within the axial length of the second planetary gear unit 4.

[0065] An oil pressure actuator 90 for the second brake is provided onthe rear side of the second brake B2. The actuator 90 has a cylindermember 91, that is fixed to and positioned on the inner peripheralsurface of the transmission case 9, and a piston member 92 that isfitted within cylinder member 91 in an oil-tight manner. While the otherpiston members 69 and 83 that extend toward the brake have extendedportions that hold the return springs 73 and 85 between comb teeth, thepiston member 92 has a shorter structure without such an extendedportion. The oil pressure actuator 90 is positioned so that a portionthereof overlaps a rear edge portion of the second planetary gear unit 4on the rear side of the second brake B2, or the front edge portion ofthe piston member 92 and the second planetary gear unit 4 are axiallyaligned. The brake plate 87 and the inner brake disks 89 of the secondbrake B2 are notched on their outer peripheries at specified intervals,and a return spring 96 is compressed between a support plate 95, thatdepends from the front edge of a skirt portion of the piston member 92,and a notched portion 93 on a fixed member such as the transmissioncase.

[0066] The third one-way clutch F3 is provided on the rear side of theoil pressure actuator 90 for the second brake B2, in other words,between the second planetary gear unit 4 and the third planetary gearunit 5. A rear carrier plate 97 of the second planetary gear unit 4 anda ring gear R3 of the third planetary gear unit 5 are connected via aconnection member 99. The third one-way clutch F3 has an outer race 100that is the fixed side and an inner race 101 that is the movable side,the outer peripheral surface of the outer race 100 is spline-engagedwith the transmission case 9, and the inner peripheral surface of theinner race 101 is spline-engaged with the boss 99 a on the connectionmember 99.

[0067] The outer race 100 described above is widened where it engages anengagement member 102, such as a roller or a sprag, according to thewidth of the engagement member. In addition, the outer race 100 isgradually narrowed both axially front to rear and radially butward, andextends in the shape of a collar only at its radially outer end on therear side. Consequently, the outer race 100 has a contact surface thatmatches the engagement member 102 which is relatively axially long, anda specified length of the transmission case is taken by theaforementioned collar shaped extended portion to provide the requiredtorque capacity. The front side of outer race 100 includes a concaveportion 100 a, and the rear portion of the actuator 90 for the secondbrake is received in the concave portion 100 a, making it possible toposition the second brake, including its actuator 90, on the outer(radially outward) side of the second planetary gear unit 4 (so that atleast a portion thereof axially overlaps the second planetary gear unit4). This contributes to the shortening of the overall axial length ofthe automatic transmission 1. In other words, the oil pressure actuator90 is positioned, between the second planetary gear unit 4 and the thirdone-way clutch F3.

[0068] The inner race 101 described above broadens where it engages theengagement member 102 in accordance with the width of the engagementmember, and narrows gradually radially inward. As described above, whilesecuring the torque capacity attributable to the contact area, the spacefor spline connection of the connection member 99 and the rear carrierplate 97 is allowed for.

[0069] The third planetary gear unit 5 is provided on the rear side ofthe third one-way clutch F3. The third planetary gear unit 5 is a simpleplanetary gear unit, and its ring gear R3 is engaged with the outerperipheral surface of a flange 99 b of a connection member 99 andconnects with the carrier CR2. The sun gear S3 is integrally formed on arear portion of the intermediate shaft 31, and a carrier CR3 thatsupports a pinion P3 is integrally formed with an output shaft 105. Theintermediate shaft 31 has a stepped structure in which the diametersequentially decreases toward the front, with the sun gear S3 portion asthe largest diameter. The carrier CR3 is formed as a flange at the frontend of the output shaft 105. A rear end projection 31 a of theintermediate shaft 31 is fitted into a front end hollow portion 105 a ofthe output shaft 105 and the output shaft 105 is rotatably supported sothat it cannot axially move. Further, the front end of the intermediateshaft 31 is fitted to the input shaft 12 (refer to FIG. 3) and isthereby rotatably supported, and both ends thereof are indirectlysupported by the transmission case 9 via the input shaft 12 and theoutput shaft 105. Also, the front end of the output shaft 105, isdirectly supported by a collar portion 9 f at the rear end 9 e of thetransmission case 9 via a bearing, and the rear end of output shaft 105is directly supported by an extension case (fixed to the rear end of thetransmission case 9, not shown) via a bearing.

[0070] The fourth brake B4 is provided on the rear side of the thirdone-way clutch F3. The fourth brake B4 is a multi-plate brake, andincludes a plurality of external brake plates 106 is engaged with aspline 9 d formed on the inner surface of the transmission case 9 alongwith the outer race 100 of the third one-way clutch F3. Further, theaxial movement of the forth brake B4 is limited by a snap ring (notshown), and inner brake disks 107 are engaged with a spline that isformed on the outer peripheral surface of the ring gear R3. The fourthbrake B4 is positioned so that the forth brake B4 and the thirdplanetary gear unit 5 axially overlap (or at least portions thereofoverlap) on the outer side of the third planetary gear unit 5.

[0071] The oil pressure actuator 109 for the fourth brake is located onthe rear side on the fourth brake B4 and the third planetary gear unit5. An oil pressure actuator 109 is a double piston type with itscylinder formed in the case 9, i.e., the inner peripheral surface of therear portion of case 9, the rear end 9 e of case 9 and the collarportion 9 f of case 9. Actuator 109 also has a first piston member 110,an intermediate support member 111 and a second piston member 112. Thefirst piston member 110 is mounted within the cylinder in an oil-tightmanner and has an extension 110 a that protrudes forward from its outerperiphery, and a hub 110 b that protrudes backward from its innerperiphery. The extension 110 a is engaged with the inner spline 9 d andopposes the fourth brake B4.

[0072] The inner periphery of the intermediate support member 111 slideson and seals with hub portion 110 b, and its outer periphery seals withthe aforementioned cylinder formed in the transmission case 9. The outerperiphery of the second piston member 112 slides and seals on the innersurface of a skirt extending from the outer periphery of support member111 and its inner periphery slides and seals on case portion 9 e andcontacts the hub portion 110 b of the first piston member 110. A returnspring 113 is compressed between the first piston member 110 and asupport plate 114 that is provided on the collar portion 9 f of thetransmission case 9.

[0073] Consequently, the oil pressure actuator 109 for the fourth brakehas a large pressure-receiving surface area and is formed in part by therear end surface of the transmission case 9. Because of the doublepiston structure that is made up of the first and second piston members110 and 112, an even larger pressure-receiving surface area is obtained,and a large force that corresponds to the set torque capacity of thefourth brake B4 is obtained.

[0074] A parking gear 115 is integrally provided on the radial outerside of the carrier CR3, and engagement of the parking gear 115 by aparking shaft 116, that extends through the transmission case, fixes theoutput shaft 105. Also, the first piston member 110 of the oil pressureactuator 109 for the fourth brake receives the parking gear 115 and hasa notch through which the parking shaft 116 extends, and is positionedon the rear side so as to slightly axially overlap the third planetarygear unit 5 on the radially outward side of the third planetary gearunit 5.

[0075] Next, the operation of the multi-speed change mechanism 6, havingthe structure described above will be described with reference to FIGS.5-7.

[0076] The multi-speed change mechanism 6 is divided by function into afront gear set 130 that is made up of the first planetary gear unit 3,and a rear gear set 131 that is made up of the second planetary gearunit 4 and the third planetary gear unit 5. The rear gear set 131 has atotal of four rotational elements, a first rotational element 137 thatis made up of both the sun gears S2 and S3 that are connected via theintermediate shaft 31, a second rotational element 136 that is made upof the carrier CR2 and the ring gear R3 that are connected via aconnection member 99, a third rotational element 135 that is made up ofring gears R1 and R2 that are connected, and a fourth (output)rotational element 138 that is made up of the carrier CR3 that isconnected to the output shaft 105.

[0077] The first rotational element 137 is connected via theintermediate shaft 31 to the first clutch C1 that is positioned on theradial inner side of the clutch section 23. The second rotationalelement 136 is connected via the second sleeve shaft 43 to the secondclutch C2 that is positioned at the forward side and on the outer radialside of the clutch section 23. The sun gear S I that is the inputelement of the first planetary gear unit 3 is connected via the thirdsleeve shaft 46 to the third clutch C3 that is positioned at the rearside and on the radially outer side of the clutch section 23.

[0078] In the first forward speed (first speed: 1st), as shown in FIG.6, while the first clutch C1 is engaged, the third one-way clutch F3 isoperated, and the input shaft 12 and the sun gears S2 and S3 (the firstrotational element 137) are connected. The reverse rotation of thecarrier CR2 and the ring gear R3 (the second rotational element 136) isstopped by the third one-way clutch F3, and the rotation (RIN) of theinput shaft 12 is directly input to the sun gear S3 of the thirdplanetary gear unit 5 via the first clutch C1. Then, due to the brakingof the ring gear R3 (stopped) by the third one-way clutch F3, the stateshown as L1 in the speed diagram in FIG. 7 is established, and aclockwise first speed is produced from the carrier CR3 (the outputrotational element 138) to which the output shaft 105 is connected.Further, the sun gear S2 rotates, but the second planetary gear unit 4idles.

[0079] In the above-described L1 state the first speed and large torqueis supported by the third one-way clutch F3, which, as shown in FIG. 4,is positioned in the relatively long space between the second and thirdplanetary gear units 4 and 5, given the large engaging surface areas ofthe holding member (roller or sprag) 102, of the outer race 100 and ofthe inner race 101. Therefore, a large torque is reliably transmitted.Also, in this state the first clutch C1 is independently operated by thefirst oil pressure actuator on the radial inner side of the clutchsection 23.

[0080] In the second-forward speed (second speed: 2nd), as shown in FIG.6, in addition to the engagement of the first clutch C1 (engaged duringthe first speed), the third brake B3 is engaged, and the operation ofthe third one-way clutch F3 is canceled, and the first and secondone-way clutches F1 and F2 are operated. In this state, the firstplanetary gear unit 3 is stopped because its carrier CR1 is stopped bythe first one-way clutch F1 that is in a locked state, and because thesun gear S1 is stopped due to locking of the second one-way clutch F2 byengagement of the third brake B3. Consequently the ring gear R2 of thesecond planetary gear unit 4 that is connected to the ring gear R1 isstopped.

[0081] The rotation of the input shaft 12 is input to the secondplanetary gear unit 4 from the sun gear S2 via the first clutch C1, andis input to the third planetary gear unit 5 via the sun gear S3. Therotation of the ring gear R2, as described before, is stopped (the speedis zero), the state indicated as L2 in the speed diagram of FIG. 7 isestablished, and clockwise second speed rotation is output from thecarrier CR3 that is connected to the output shaft 105.

[0082] In state L2 described above, the rotational torque of the ringgear R2 is divided and supported by the third brake B3 via the first andsecond one-way clutches F1 and F2. Because the torque capacity of thefirst one-way clutch F1 is used, the torque load capacities and sizes ofthe second one-way clutch F2 and the third brake B3 can be reduced.Thus, it is possible to collectively position the third brake B3 and theoil pressure actuator 66, as well as the first and second one-wayclutches F1 and F2, in a compact manner on the forward portion of thefirst planetary gear unit 3.

[0083] In the third forward speed (third speed: 3RD), as shown in FIG.6, in addition to the engagement of the first clutch C1 (engaged duringthe first and second speeds), the third clutch is engaged, the operationof the second one-way clutch F2 is canceled, and. the operation of thefirst one-way clutch F1 is maintained. In this state, the rotation ofthe input shaft 12, which has been input to the rear gear set 131 viathe first clutch C1, is additionally input to the sun gear S1 of thefront gear unit 130 via the third clutch C3, while the carrier CR1 isheld by the first one-way clutch F1.

[0084] Then, because the rotation of the input shaft 12 is input to thesun gear S1 and the carrier CR1 is held, the first planetary gear unit 3is brought into the state shown as L3 in the speed diagram in FIG. 7,and clockwise rotation RV1 is output from the ring gear R1, serving asthe output element of the front gear set 130, to the ring gear R2 of thesecond planetary gear unit 4, serving as the input element of the reargear unit 131. Meanwhile, in the rear gear set 131, because the rotationRIN of the input shaft 2 is input to the sun gears S2 and S3, therotation RV1 that is input to the ring gear R2, as shown by L4 in FIG.7, is synthesized and third speed rotation is produced from the carrierCR3 that is connected to the output shaft 105. Further, the third brakeB3 is engaged, but since the second one-way clutch F2 is idling, thethird brake B3 is not involved in the shifting.

[0085] In the above-described L3 state, the first one-way clutch F1supports the reaction force of the torque that is transmitted to thefirst planetary gear unit 3; however, in the third speed state, becausethe torque that goes through the first planetary gear unit 3, thatserves as is the front gear unit 130, and the torque that is directlytransmitted via the first clutch C1 to the rear gear unit 131 aresynthesized, a portion of all the transmitted torque is sufficient forthe reaction force torque that is borne by the first one-way clutch F1.Consequently, as the first one-way clutch F1, a compact one-way clutchwith a small torque capacity is sufficient, and it is possible tocollectively position the other holding units, the third brake B3 andthe second one-way clutch F2 in a relatively small space ahead of thefirst planetary gear unit 3.

[0086] Also, the third clutch C3 is engaged by supply of oil pressure tothe third oil pressure actuator which causes the third piston 53 to moveaxially forward, and the extension 53 d of the back side of the thirdpiston 53 presses the drive plates 40 and the driven disks 41 of thethird clutch C3 from the back side toward the front side. As describedbefore, the second clutch C2 shares the clutch drum 37 with the thirdclutch C3, and all of the drive plates 39 and 40 are axially alignedwith and engaged by the spline 37 a on the inner surface of the clutchdrum 37. However, because the second piston 47 and the third piston 53are operated independently, the operation of the third clutch C3 doesnot affect the second clutch C2.

[0087] In the fourth forward speed (fourth speed: 4TH), as shown in FIG.6, in addition to the engagement of the first clutch C1 (engaged duringthe first, second and third speeds) and the engagement of the thirdclutch C3 (engaged during the third speed), the second clutch C2 isengaged, and the operation of the first one-way clutch F1 is canceled.In this state, the rotation of the input shaft 12, which has been inputto the sun gears S2 and S3 of the rear gear unit 131 via the firstclutch C1, is additionally input to the carrier CR2 and the ring gear R3via the second clutch C2. Then, the rear gear set 131, in other wordsboth of the second and third planetary gear units 4 and 5, directlyrotates, the state indicated as L5 in FIG. 7 is established, and thefourth speed rotation is output from the carrier CR3 that is connectedto the output shaft 105.

[0088] In the above-described L5 state, the third clutch C3 and thethird brake B3, as shown in FIG. 6, are engaged. However, because therotation of the input shaft 12 is transmitted to the sun gear S1 via thesecond clutch C2 and the second planetary gear 4 unit is directlyconnected to the input shaft 12 and rotates clockwise, the rotation ofthe input shaft 12 is also input to the ring gear R1 that is connectedto the ring gear R2 to establish the state shown as L6 in FIG. 7, andthe entire first planetary gear unit 3 (front gear set 130) idles in astate of direct connection. Also, in the fourth speed state, the frontgear set 130 and the rear gear set 131 are both directly connected, andthe first through fourth holding units, in other words, the firstthrough fourth brakes B1 through B4 and the first through third one-wayclutches F1 through F3, do not operate and the reaction force is notsupported.

[0089] Also, the second clutch C2 is connected by supply of oil pressureto the second oil pressure actuator which causes the second piston 47 tomove axially forward so that its skirt portion 47 a presses against thedrive plates 39 and the driven disks 41. The third clutch C3 ismaintained in the engaged state because the operation of the secondclutch C2 does not affect the engagement state of the third clutch C3.

[0090] In the fifth forward speed (fifth speed: 5TH), as shown in FIG.6, the first clutch C1 is disengaged, while the engagement of the secondand third clutches C2 and C3 is maintained, and the first brake B1 isengaged. In this state, the rotation-of the input shaft 12 is input viathe second clutch C2 to the carrier CR2 of the second planetary gearunit 4 (rear gear set 131) and the ring gear R3 of the third planetarygear unit 5, and is input via the third clutch C3 to the sun gear S1 ofthe first planetary gear unit 3. Then, because the carrier CR1 is heldby the first brake B1, the front gear set 130 is brought into the stateshown as L3 in FIG. 7, and the decelerated clockwise rotation RV1 isoutput to the ring gear R2 of the rear gear set 131 from the ring gearR1. As described before, because the rotation of the input shaft 12 isinput to the carrier CR2 and the ring gear R3 of the rear gear unit 131,a state shown as L7 in FIG. 7 is established, and fifth speed rotationis output to the output shaft 105 from the carrier CR3. At this time,the third brake B3, as shown in FIG. 6, is engaged. However, because thesecond one-way clutch F2 is idling, the third brake B3 is not involvedin the shifting.

[0091] In fifth speed, the first brake B1 bears the reaction force ofthe transmitted torque. However, because the fifth speed is a high-speedstate, a small torque capacity is sufficient. Further, because thetorque from the path that goes through the second clutch C2 and from thepath that goes through the third clutch C3 is synthesized by the ringgear unit 131 and transmitted to the output shaft 105, a portion of theoverall transmitted torque is sufficient for the torque capacity of thefirst brake B1 that brakes the carrier CR1 and the ring gear R1.Further, even a small torque capacity is sufficient. Consequently, thefirst brake B1 can be relatively axially short and can be located on theouter side of the first planetary gear unit 3, and the oil pressureactuator 81 can also be provided in a space which is relatively axiallyshort and small, and which straddles the adjacent first and secondplanetary gear units 3 and 4 on their outer side. Thus, it is possibleto provide the third brake B3 and the oil pressure actuator 81 in arelatively small space on the radially outer side of the first planetarygear unit 3.

[0092] In the first clutch C1, because the first piston 32 is urgedforward in the axial direction by the return spring 35, the pressure ofthe drive plate 27 and the driven disk 29 is canceled by release of oilpressure from the first oil pressure chamber 33 of the first oilpressure actuator. During release, the first clutch drum 26 rotates at arelatively high speed and therefore centrifugal force acts on the oil inthe first cancel chamber 36, and the oil pressure in the first oilpressure chamber 33 is quickly discharged.

[0093] In sixth speed (6TH), as shown in FIG. 6, the third clutch C3 isreleased, the engagement of the second clutch C2 is maintained, and thesecond brake B2 is engaged. In this state, the rotation of the inputshaft 12 is input to the carrier CR2 of the second planetary gear unit 4that serves as the rear gear set 131 and to the ring gear R3 of thethird planetary gear unit 5 via the second clutch C2. Meanwhile, becausethe ring gear R2 is held by the second brake B2, the sun gears S2 and S3rotate clockwise at a speed higher than in fifth speed due to therotation of the carrier CR2. Sixth speed rotation that is faster thanfifth speed is transmitted to the output shaft 105 from the carrier CR3by the rotation of the ring gear R3 and the high speed rotation of thesun gear S3. The sixth speed corresponds to L8 of the speed diagram inFIG. 7. In sixth speed, the first and third brakes B1 and B3 are engagedas shown in FIG. 6. However, because the first and second one-wayclutches F1 and F2 are idling, the first and third brakes B1 and B3 arenot involved in the shifting. Also, although the third clutch C3 isdisengaged, the oil pressure in the third oil pressure chamber isquickly released due to the centrifugal force that acts on the oil inthe third cancel chamber 57.

[0094] Also, when in the sixth speed, the second brake B2 bears thereaction force of the transmitted torque. However, because the sixthspeed is a high-speed state that is higher than the fifth speed, even as -mall torque capacity is sufficient. Consequently, as in the case ofthe first brake B1, the second brake B2 can be relatively axially shortand located on the outer side of the second planetary gear unit 4, andthe oil pressure actuator 90 can also be provided in a space which isrelatively axially short and small, on the front side of the thirdone-way clutch F3.

[0095] As clearly shown in FIG. 6, the shifting from the first throughthe fourth speeds is carried out by the one-way clutch, and the shiftingfrom the fourth speed to the fifth speed and the shifting from the fifthspeed to the sixth speed is carried out by clutch to brake shifting.

[0096] In downshifting, the second clutch C2 or the third clutch C3 isoperated, as. shown in FIG. 6, i.e., when downshifting from the sixthspeed to the fifth speed, from the fourth speed to the third speed, andfrom the third speed to the second speed.

[0097] In all shifts, the second and third pistons 47 and 53 of thesecond and third oil pressure actuators are each independently operated,and because their drive plates 39 and, 40 and driven disks 41 and 44 canbe independently engaged and disengaged, the operation of one of theclutches does not affect the operation-or engaged state of the otherclutch.

[0098] In reverse (reverse speed: REV), as shown in FIG. 6, the thirdclutch C3 is engaged, and the fourth brake and the first one-way clutchF1 are engaged. In this state, because the rotation of the input shaft12 is input to the sun gear S1 of the front gear set 130 via the thirdclutch C3, and because the carrier CR1 is held by the first one-wayclutch F1, the state shown as L3 in FIG. 7 is established, and theclockwise output rotation RV1 is transmitted to the ring gear R2 of therear-gear set 131 from the ring gear R1. Because the ring gear R3 andthe carrier CR2 are held by the fourth brake B4, the rear gear unit 131is brought into state L10 in FIG. 7, and reverse rotation is transmittedto the output shaft 3 from the carrier CR3.

[0099] In reverse a large torque that has been decelerated acts on thefourth brake B4 that holds the ring gear R3 and the carrier CR2. Thefourth brake B4 is made relatively axially long and overlaps the thirdplanetary gear unit 5 on the outer side of the third planetary gear unit5 and, because its oil pressure actuator 109 includes a relatively widepressure receiving surface area on the rear end 9 e of the transmissioncase 9 and has a double piston structure, a large force can be applied,making it possible to reliably support the torque corresponding to thelarge reaction force.

[0100] During engine braking (coasting), as shown in FIG. 6, when inthird speed and in reverse, the first brake B1 is engaged, and thecarrier CR1 is reliably held, while the first one-way clutch F1 idles.When in second speed the second brake B2 is engaged, and the ring gearR2 is reliably held. Further, when in first speed, the fourth brake B4is engaged and the ring gear R3 is reliably held.

[0101] Further, during engine braking in second speed, in addition tothe second brake B2 which is primarily used for engine braking, thefirst brake B1 is engaged, the ring gear R2 is held by the first brakeB1 via the carrier CR1, and thus the torque capacity required of thesecond brake B2 is made small, making it possible to make the secondbrake B2 smaller. The second brake B2 is for use in engine braking whenin second speed. The torque capacity of the second brake B2 can besmall, and a relatively small space in the outer portion of the secondplanetary gear unit 4 is sufficient to accommodate brake B2. Further, asdescribed above, at the time of engine braking of the second speed, ifthe first brake B1 is operated, the torque capacity of the second brakeB2 can be smaller. The second brake B2 can be positioned along with itsoil pressure actuator 90 in a small space, and can effect braking withcertainty and high reliability.

[0102] As described above, when the torque from the input shaft 12 isinput to the second planetary gear unit 4, the input torque from the sungears S2 and S3 when in the second speed, from the sun gears S1, S2 andS3 when in the third speed, from the sun gears S2 and S3 when in thefourth speed, from the sun gears S1 and S2 and the ring gear R3 when inthe fifth speed, and from the sun gears S2 and S3 and the ring gear R3when in the sixth speed, is transmitted to the front gear set 130 and tothe rear gear set 131. Consequently, the input torque is not inputsolely to the second planetary gear unit 4, and thus the secondplanetary gear unit 4 is made smaller in order to achieve theappropriate gear ratio. In addition, it is possible to make it smallerdue to the lower strength required because of the distribution of thetorque input. Although the oil actuator 81 is positioned on the outerside of the second planetary gear unit 4, and the second planetary gearunit 4 has a torque capacity that supports the torque required for thefirst brake B1, it is possible to make the transmission more compact inboth its axial and radial dimensions.

[0103] Also, with regard to the first, second and third clutches C1, C2and C3 that transmit the input torque to the first, second and thirdplanetary gear units 3, 4 and 5, in order to sufficiently maintain thetorque capacity it is desirable to increase the radial dimensions.However, because clutch section 23 is positioned on the torque converter2 side of the multi-speed change mechanism, the clutches can bestructured so that their respective radial dimensions decrease towardthe output shaft. Thus, a transmission with an overall shape suitablefor installation in a vehicle, as a FR automatic transmission, can beobtained.

[0104] While the first embodiment described above was explained withreference to a multi-speed change mechanism, the invention can beapplied to any other automatic speed change mechanism, as long as themechanism has at least three clutches which are closely positioned.

[0105] Second Embodiment

[0106]FIG. 8 shows a second embodiment of the invention and correspondsto FIG. 3 of the first embodiment. Further, in the followingexplanation, the elements and functions are different from the firstembodiment will be explained, and explanation of elements and functionsthat are the same will be appropriately omitted.

[0107] As in the first embodiment, in the second embodiment of theinvention, a fourth clutch C4 is positioned on the front side of thefirst clutch C1 so that the fourth clutch C4 and the first clutch C1 areaxially aligned. In addition, the members on the input side of the firstand fourth clutches C1 and C4 are integrally formed, and the members onthe output side of the fourth clutch C4 and the sun gears S2 and S3 ofthe second and third planetary gear units 4 and 5 are also integrallyformed. Further, a fourth one-way clutch (one-way clutch) F1 isinterposed between the output side members of the first clutch C1 andthe output side members of the fourth clutch C4.

[0108] As shown in FIG. 8, in the second embodiment, a first clutch drum140 of a first clutch C1 has a flange portion 140 a that is fixed to therear end of the sleeve 25 whose inner diameter side is engaged with theoutput shaft 12, and a drum portion 140 b that extends from flangeportion 140 a to the back side (rear). A spline 140 c is formed on theinner peripheral surface of the drum portion 140 b, and plural drivenplates (outer friction plates) 141 of the first clutch C1 are engagedwith the rear half portion of the spline 140 c so as to be axiallymovable. The driven disks (inner friction plates) 142 that are engagedand disengaged with these drive plates 141, are engaged with a spline143 a that is formed on an outer peripheral surface of an outer race 143of the fourth one-way clutch F0. An inner race 144 of the fourth one-wayclutch F1 is spline-engaged with the outer peripheral surface of theintermediate shaft 31.

[0109] Fourth clutch C4 has a fourth clutch drum 145 provided on theinner side of the first clutch drum 140. The fourth clutch drum 145 hasa flange portion 145 a fixed at its inner periphery to the peripheralsurface of the output shaft 12, and a drum portion 145 b that extendsfrom the flange portion 145 a to the back side. A spline 145 c is formedon the inner peripheral surface of the drum portion 145 b, and pluraldrive plates 146 of the fourth clutch C4 are engaged with the spline 145c so as to allow for axial movement. Driven disks 147, that are engagedand disengaged with the drive plates 146, are engaged with a spline 149a, formed on the outer peripheral surface of a fourth hub 149, so as tobe axially movable. The inner side of the fourth hub 149 is fixed to theouter peripheral surface of the input shaft 12.

[0110] Splines (not shown) formed on the outer peripheral surface of thedrum portion 145 b of the fourth clutch drum 145 are engaged with thesplines 140 c of the drum portion 140 b of the first clutch drum 140. Anend edge 145 d of the drum portion 145 b is positioned so as to opposethe front side of the first clutch C1. The entire fourth clutch drum 145is movably supported for axial movement by the first clutch drum 140 andthe output shaft 12. An oil-tight fourth oil pressure chamber 150 isformed between the front side of the flange portion 145 a and the backside of the flange portion 140 a of the first clutch drum 140. Thefourth clutch drum 145, in addition to serving as the clutch drum of thefourth clutch C4, also acts as the piston of the first oil pressureactuator that engages and disengages the first clutch C1.

[0111] A fourth piston 151 of the fourth oil pressure actuator isprovided on the inner side of the fourth clutch drum 145. The fourthpiston 151 has a flange portion 151 a and a drum portion 151 b, and issupported for axial movement by the fourth clutch drum 145 and theperipheral surface of the input shaft 12. The fourth piston 151 ispositioned so that an edge 151 c of the drum portion 151 b opposes thefront side of the fourth clutch C4, and an oil-tight fourth oil pressurechamber 152 is formed between the front side of the flange portion 151 aand the back side of the flange portion 145 a of the fourth clutch drum145.

[0112] A fourth cancel plate 153, having its inner periphery fixed tothe outer peripheral surface of the output shaft 12, is provided on theback side of the fourth piston 151. A return spring 154 is compressedbetween the front side of the cancel plate 153 and the backside of thefourth piston 151 which define a fourth cancel chamber 155 therebetween.

[0113] Next, operation of the multi-speed change mechanism 6 will beexplained with reference to FIGS. 9 and 10. Further, because theoperations other than those of the first and fourth clutches C1 and C4and the fourth one-way clutch F1 are the same as in the firstembodiment, duplicate explanation will be appropriately omitted, andmainly operation of the first and fourth clutches C1 and C4 and thefourth one-way clutch F0 will be explained.

[0114] As shown in FIG. 9, in this second embodiment, the first clutchC1 and the fourth clutch C4 are disposed between the input shaft 12 andthe intermediate shaft 31, and, further, the fourth one-way clutch F1 isinterposed between the first clutch C1 and the intermediate shaft 31.

[0115] If the operational table in FIG. 10 of this second embodiment iscompared with the operational table in FIG. 6 of the first embodiment,it can be understood that in this embodiment, in the first throughfourth speeds, the fourth clutch C4 is engaged only when engine braking,and the fourth one-way clutch F1 is engaged. Because of this difference,in this embodiment, shifting from the fourth speed to the fifth speed,which is clutch to brake shifting in the first embodiment, can besmoothly performed using a one-way clutch. Also, while torquetransmission with engine braking in the first through fourth speeds isthrough the first clutch C1 in the first embodiment, in this secondembodiment it can be through both the first and fourth clutches C1 andC4. Consequently, it is possible to make the first clutch C1 and thefirst oil pressure actuator that operates it more compact.

[0116] Further, while the second embodiment has been explained withreference to the multi-speed change mechanism 6, this second embodimentis applicable to any automatic speed change mechanism so long as themechanism has a clutch section 23 having at least four clutches whichare closely positioned.

[0117] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresent embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

[0118] The disclosure of Japanese Patent Application No. 2001-391423filed on Dec. 25, 2001, including the specification, drawings andabstract, is incorporated herein by reference in its entirety.

What is claimed is:
 1. An automatic transmission for changing a torque transfer path through a gear section, to thereby change rotational speed of an input member to one of a plurality of shift speeds, and transmitting the rotation at the one shift speed to an output member using a clutch and a holding unit, said automatic transmission having axially opposed front and rear ends and comprising: at least a first clutch, a second clutch and a third clutch which transmit the rotation of the input member to different rotational elements of the gear section, and which are engaged when moving forward and are positioned together with a first oil pressure actuator, a second oil pressure actuator, and a third oil pressure actuator, respectively, to form a clutch section; wherein the second and third clutches are axially aligned so that the rear end side of the second clutch and the front end side of the third clutch oppose each other, and the first clutch is located radially inside the second and third clutches; and wherein a clutch drum is axially extended to accommodate both the second and third clutches, and wherein by engaging and disengaging the second clutch from the front end side using a second piston of the second oil pressure actuator, and by engaging and disengaging the third clutch from the rear end side using a third piston of the third oil pressure actuator, the first, second and third clutches are separately engaged and disengaged by the first, second and third oil pressure actuators, respectively.
 2. The automatic transmission according to claim 1, wherein the clutch drum has a flange on the front end side which is sandwiched between a second piston of the second oil pressure actuator and wherein a third piston of the third oil pressure actuator has a portion extending axially toward the rear end along an external surface of said drum to a portion for engaging the third clutch from its rear end side.
 3. The automatic transmission according to claim 2, wherein a second oil pressure chamber is formed between the flange portion of the clutch drum and the second piston, and a third oil pressure chamber is formed between the flange portion and the third piston.
 4. The automatic transmission according to claim 3, wherein by removing the oil pressure of the third oil pressure chamber while the second and third clutches are engaged, the third clutch is disengaged and the rotational speed of the input member is changed to the highest of the plurality of shift speeds, which highest speed is transmitted to the output member.
 5. The automatic transmission according to claim 1, wherein the first clutch is located radially inward of the third clutch and axially overlaps the third clutch.
 6. The automatic transmission according to claim 5, wherein a third hub of the third clutch is positioned radially inward of the third clutch, a second hub of the second clutch is positioned radially inward of the third hub, and the first clutch is positioned radially inward of the second hub.
 7. The automatic transmission according to claim 6, wherein the first clutch is engaged at or below a forward speed at a direct connection stage, the second clutch is engaged at or above the forward speed at the direct connection stage, and the third clutch is engaged in at least one of the forward speeds and in the reverse speed, whereby the automatic transmission has at least five forward speeds and one reverse speed.
 8. The automatic transmission according to claim 7, wherein the first clutch is engaged in first through fourth forward speeds, the second clutch is engaged in at least the fourth and fifth forward speeds, and the third clutch is engaged in the third and fifth forward speeds and in the first reverse speed.
 9. The automatic transmission according to claim 8, wherein a first piston of the first actuator is provided on the front end side of the first clutch, and radially inward of the second clutch.
 10. The automatic transmission according to claim 9, further comprising: a first cancel plate that forms a first cancel chamber in cooperation with the first piston and is positioned on the rear end side of the first piston; a flange portion of the first clutch drum that forms the first oil pressure chamber in cooperation with the first piston and is positioned on the front end side of the first piston; a second cancel plate of the second actuator that is positioned on the front end side of the flange portion of the first clutch drum; a second piston that forms a second cancel chamber in cooperation with the second cancel plate and is positioned on the front end of the second cancel plate; and a flange portion of the clutch drum of the second and third clutches that forms the second oil pressure chamber in cooperation with the second piston and is positioned on the front end side of the second piston.
 11. The automatic transmission according to claim 8, further comprising a first planetary gear unit that is a dual planetary gear unit and second and third planetary gear units that are simple planetary gear units, the first, the second, the third planetary gear units being interposed between the first, the second, the third clutches and the output member; and first, second, third and fourth holding units that-are engaged and disengaged with rotational elements of the first, the second and the third planetary gear units, respectively, wherein: a member on the output side of the first clutch is integral with a sun gear of the second and the third planetary gear units; a member on the output side of the second clutch is integral with a carrier of the second planetary gear unit and a ring gear of the third planetary gear unit is engaged and disengaged by the fourth holding unit; a member on the output side of the third clutch is integral with a sun gear of the first planetary gear unit which is engaged and disengaged by the third holding unit; the first holding unit is engaged with and disengaged from a carrier of the first planetary gear unit; ring gears of the first and the second planetary gear units are integrally formed and engaged and disengaged by the second holding unit; a carrier of the third planetary gear unit is integrally formed with the output member; a first forward speed is achieved by engagement of the first clutch and the fourth holding unit; a second forward speed is achieved by engagement of the first clutch and the first and third holding units;, a third forward speed is achieved by engagement of the first: and third clutches and the first holding unit; a fourth forward speed is achieved by engagement of the first and second clutches; a fifth forward speed is achieved by engagement of the second and third-clutches and the first holding unit; and a reverse speed is achieved by engagement of the third clutch and the first and fourth holding units.
 12. The automatic transmission according to claim 11, wherein a sixth forward speed is achieved by engagement of the second clutch and the second holding unit.
 13. The automatic transmission according to claim 12, wherein the fourth clutch is axially aligned with and positioned on the front side of the first clutch, the members on the output side of the first and fourth clutches are integrally structured, the member on the output side of the fourth clutch and the sun gears of the second and the third planetary gear units are integrally structured, and a one-way clutch is interposed between the member on the output side of the first clutch and the member on the output side of the fourth clutch.
 14. The automatic transmission according to claim 12, wherein the fourth clutch is axially aligned with and positioned on the front side of the first clutch, the members on the output side of the first and fourth clutches are integrally structured, the member on the output side of the fourth clutch and the sun gears of the second and the third planetary gear units are integrally structured, and a one-way clutch is interposed between the member on the output side of the first clutch and the member on the output side of the fourth clutch.
 15. An automatic transmission for changing a torque transfer path through a gear section, to thereby change rotational speed of an input member to one of a plurality of shift speeds, and transmitting the rotation at the one shift speed to an output member using a clutch and a holding unit, said automatic transmission comprising: at least a first clutch and a second clutch which transmit the rotation of the input member to different rotational elements of the gear section, and which are engaged when moving forward and are positioned together with a first oil pressure actuator and a second oil pressure actuator, respectively, to form a clutch section; wherein the first and second clutches are axially aligned; wherein a clutch drum is axially extended to accommodate both the first and second clutches; wherein said first oil pressure actuator includes a first piston which engages the first clutch by pressing against the first clutch at one axial end of the axially aligned second and third clutches and said second oil pressure actuator includes a second piston which engages the second clutch by pressing against the second clutch at a second axial end, opposite said first axial end, of the axially aligned first and second clutches.
 16. An automatic transmission for changing a torque transfer path through a gear section, to thereby change rotational speed of an input member to one of a plurality of shift speeds, and transmitting the rotation at the one shift speed to an output member using a clutch and a holding unit, said automatic transmission comprising: at least a first clutch, a second clutch and a third clutch which transmit the rotation of the input member to different rotational elements of the gear section, and which are engaged when moving forward and are positioned together with a first oil pressure actuator, a second oil pressure actuator, and a third oil pressure actuator, respectively, to form a clutch section; wherein the second and third clutches are axially aligned and the first clutch is located radially inside the second and third clutches; wherein a clutch drum is axially extended to accommodate both the second and third clutches; wherein the third oil pressure actuator includes a third piston, said third piston having a head portion in an operating chamber of said third oil pressure actuator located at a first axial end of the axially aligned second and third clutches, having an engaging element located at a second axial end, opposite said first axial end, of the axially aligned second and third clutches, and having a connection portion connecting said head portion and said engaging element; and wherein by engaging and disengaging the second clutch from the first axial end side using a second piston of the second oil pressure actuator, and by engaging and disengaging the third clutch from the second axial end side, opposite said first axial end side relative to the axially aligned second and third clutches, using the engaging element of the third piston of the third oil pressure actuator, the first, second and third clutches are separately engaged and disengaged by the first, second and third oil pressure actuators, respectively.
 17. The automatic transmission according to claim 16, wherein said connection portion of the third piston extends from said head portion axially along an external surface of said drum to said engaging element for engaging the third clutch from its second axial end side. 